Machine tool control system and method

ABSTRACT

A machine tool control method wherein a supervising computer is operated to observe acceleration and deceleration characteristics of the particular control system and then to compute optimum deceleration points with respect to subsequent commands to the system on the basis of the observed characteristics and to initiate deceleration of the system at the optimum points in executing the successive commands to the system.

United States Patent 1191 Slawson 1 Apr. s, 1975 1 1 MACHINE TOOLCONTROL SYSTEM AND METHOD {75] Inventor: Kenneth Leonard Slawson. Depew.N.Y. [731 Assignee: Haudaillelndustrles. Ines, Buffalo.

[22] Filed: Dec. 20. 1973 211 Appl. No.: 426.591

Related US. Application Data 162] Division at Ser. No. 150.637, June 7.1971 Pat. No.

311116.723. which is a division of Scr. No. 811L131. June 6. 1969. Pat.No. 3.629560.

[52] U.S.Cl. 235/l5l.11:318/561;318/571 [51] Int. Cl. G06b 15/46; GOSb19/28 [58] Field 01 Search 235/l51.l1; 318/561, 570. 318/571. 573. 574,568, 601, 591. 603;

[56] References Cited UNITED STATES PATENTS 3.344.260 9/1967 Lukens318/571 X (use;

Ml1 M10 rem Fredriksen 318/561 3.486.012 12/1969 Burnett et a1235/l$1.11 1617.715 11/1971 Dummermuth 318/571 3.727.191 4/1973 McGee235/151.ll 3.748.563 7/1973 Pomella et a1.. 318/571 X PrimaryBummer-Joseph F. Ruggiero Attorney. Agent, or Firm-Hill. Gross. Simpson.Van Santcn. Steadman. Chiara & Simpson [57] ABSTRACT A machine toolcontrol method wherein a supervising computer is operated to observeacceleration and deceleration characteristics of the particular controlsystem and then to compute optimum deceleration points with respect tosubsequent commands to the system on the basis of the observedcharacteristics and to initiate deceleration of the system at theoptimum points in executing the successive commands to the system.

16 Claims, 15 Drawing Figures CWl/EE I If CM) 1067C V w I x ii ria w jIT I c M MA QT/9W5 PATENTEUAPR ems smear? FATENTEBAPR ems 87G saw 5 or 7Fig 101) rear owe/46: 37025 PI'JENTEUAPR 8W5 v V 3 75.573;

' 211m B or 1 aware/err K123 zwggrem MACHINE TOOL CONTROL SYSTEM ANDMETHOD CROSS REFERENCES TO RELATED APPLICATIONS The present applicationis a division of my pending application Ser. No. l50,637 filed June 7,I971, now U.S. Pat. No. 3,8l6,723. Saidapplication Ser. No.

l50,637 refers under 35 USC I20 to my earlier applifiled July 12, I967(now abandoned) and Ser. No.

744.392 lfiled July l2. I968, (now U.S. Pat. No. 3,634,662 issued Jan.ll, I972) and the disclosures of each of these applications is herebyreference in its entirety.

SUMMARY OF THE INVENTION The present invention relates to a controlsystem and method capable of determining its own individualcharacteristics such as acceleration and deceleration times anddistances under given conditions and capable of I automaticallyutilizing such observed characteristics in the optimum execution ofsubsequent commands to the system.

The invention also relates to methods and apparatus for derivingacceleration and/or deceleration characteristics for a given controlsystem for subsequent use in adjusting the operation of the controlsystem in response to successive commands.

It is an object of the present invention to provide a control systemcapable of providing more nearly opti mum operation in executing aseries of commands.

It is another object of the invention to provide a control system whichmay be adapted to the particular characteristics of a given load withwhich it is associated.

Another object of the invention is to provide a control system which mayreadily be retuned from time to time so as to maintain more nearlyoptimum operating conditions during the life of the system.

Still another and further object of the present invention is to providea control system capable of automatically determining its own currentoperating characteristics at'desired intervals and for thereafter takinginto account any changes in such operating characteristics in executingfuture commands to the system.

A more specific object of the present invention is to scription of apreferred embodiment thereof. taken in conjunction with the accompanyingdrawings, although I variations and modifications may be effectedwithout departing from the spirit and scope of the novel concepts of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagramillustrating a portion of a control system in accordance with thepresent invention;

FIG. 2 is a schematic diagram illustrating another portion of a controlsystem in accordance with the present invention;

FIG. 3 is a schematic diagram illustrating still a further portion of acontrol system in accordance with the present invention;

FIG. 4 is a graphical illustration of the response of the control systemfor the case of a relatively long move;

FIG. 5 is a graphical representation of the response of the controlsystem for the case of a relatively short move;

FIG. 6 is graphical representation of the operating characteristic of atypical numerical control system for a 2.000 inch move;

FIG. 7 is a graphical illustration of the response characteristics ofthe numerical control system for a 4.000 inch move; I

FIG. 8 is a graphical illustration showing the improved results obtainedwith the control system of the present invention;

FIG. 9 consisting of FIGS. 90. 9b and 9c is a flow diagram illustratingthe determination of acceleration and decelereation characteristics forthe control system; and

FIG. 10 consisting of FIGS. 10a, 10b and 100 and FIG. 11 consisting ofFIGS. Ila and Ila are flow diagrams showing exemplary control logic fordetermining a more nearly optinum deceleration point in executingsuccessive commands to the system. i

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a portion ofa control system in accordance with the present invention. By way ofexample, the system may be utilized to control successive punchingoperations on a punch press such as disclosed in my pending applicationsSer. No. 653,968 and Ser.

I No. 744,392. A specific transducer direction and rate sensing circuitcorresponding to component 10 of FIG. I is illustrated in the fourthFigure of said copending applications, and the overall control system isillustrated in the sixth Figure of such copending applications. During apositioning operation of such a control system, motion along the X-axis,for example results in a series of motion pulses at the output of pulseamplifier 11 or pulse amplifier 12, depending on the direction of suchmotion. As illustrated in detail in the copending applications, theoutputs of the pulse amplifiers I1 and 12 are supplied to positioningcontrol logic as represented by component 14 in FIG. 1. The positioningcontrol logic 14 includes a bidirectional counter (indicated at 30 inFIG. 3) whose initial count is set by means of a computer as illustratedin the copending applications. With the present embodiment.

however, the counter is loaded with a binary number equal to thecommanded distance of movement along the axis, S less an optimumdeceleration distance 5, The positioning control logic 14 is utilized toemit a signal at output line 15 when the distance 8 traversed by theload with respect to the given axis is equal to the total commandeddistance 8 minus the optimum deceleration distance S desired direction.

Referring to FIG. 3 of the present application, the illustrated controlsystem has provision for a command ment in the positive direction (frompunched tape for I example), the input BAG 1 from the computer may be ata logical one level, while for a negative displacement command thecomputer may place the line BAC at the logical one level. Thereafter,the computer selects components 20, FIG. 3, so as to set flip-fiop 21for a I positive command or flip-flop 22 for a negative command. For apositive command, driver 23 is activated from the set output offiip-l'lop 21, while for a negative associated axis components at amaximum rate in the When the computer receives the deceleration pointsignalvia line 15, FIG. I, the computer actuates the clear selectorcomponent 27, FIG. 3, so as to transmit a clear signal to the flip-flops21 and 22 removing the previous energizing input to the servo amplifier25.

from pulse amplifier 11 or 12 (via line 28 or 29, FIGS.

1 and 3) so that now the counter 30 will count down 1 toward zero as theload approaches the commanded end position. If the load should overshootslightly, counter 30 will begin counting up with opposite polarity inthe same way as described for the reversible counter of the priorapplications.

Since the prior applications have disclosed in detail a reversiblebinary counter such as counter 30 with a substantial number of stagesincluding a plurality of input stages such as stages 33 and 34 in FIG.3, and a sign representing stage such as stage 35, the representationolthe counter 30 in FIG. 3 will be sufficient. It will be understoodfrom the prior applications that the counter 30 is actuated by the countpulse output from amplifier 11 or 12, FIG. 1, via conductor 28 and 29and transducer logic 36, FIG. 3, and will progressively count down asthe load approaches the commanded I position. The counter 30 provides alinear analog output from converter 31 over a range of positive andnegative error counts in the vicinity of zero, and the linear range hasa sufficient extent to cover any possible overshoot of the system ineither direction of travel. The action of the converter 31 and servoamplifier within the linear error range will correspond to thatexplained in detail in the copending applications. The same reversiblebinary counter is preferably utilized both for obtaining thedeceleration point signal at line 15 and for providing the control ofconverter 31 thereafter. The analog signal at the output 37 from theconverter 31 thereafter. The analog signal at the output 37 fromconverter 31 prior to the occurrence of the decelferation point signalis not detrimental since amplifier 25 is saturated at this time. Theconverter and zero count logic component 38 is utilized to control thedigital to analog converter 31 so as to provide a linear output as afuncntion of error count as shown in the fourtheenth and fifteenthFigures of the copending application Ser. No. 744,392. 1

Referring to FIG. 3, the computer is considered as controlling loadselector components 39 and 40 and clear selector components 41 and 42 sothat the counter stages such as 33-35 can be cleared and than have thedesired optimum deceleration count inserted therein as determined by thelevels applied to the computer output conductors such as indicated at'BAC 0, BAC 10 and BAC 11.

The deceleration point signal at line 15 serves to set a decelerationpoint status flag flip-flop 43, FIG. 3, which controls NOR gates 43a and43b having output lines 430 and 43d to the Interrupt bus and skip bus ofthe computer. Also test and clear selector components 43c and 43f areprovided to enable the computer to determine that the deceleration pointinterrupt signal has occurred and to enable the computer to thereafterremove the interrupt signal from the deceleration point status flagflip-flop 43.

Referring to FIG. 3, the means for generating the deceleration pointsignal at line 15 has been indicated.

Specifically the output line 44 from component 38 corresponds to the XZero output line (1445) in the fourteenth Figure of the copendingapplication Ser. No. 744,392. This line 44 supplies a positive goingsignal when the count in counter 30 equals zero, which signal isinverted by component 45. The resultantnegative going signal at input toNOR gate 46 is transmitted to line 15 providing a control flip-flop I47has been placed in a set condition during loading of counter 30. Thecomputer will set flip-flop 47 when loading the value S=S S, but willleave the flip-flop 47 reset when loading the value S into the counter.

In the illustrated system, which may utilize the digital computerdescribed in detail in the copending applications, it is necessary todetermine a desired value of deceleration distance S so as to enable thecomputer to compute the deceleration point S equals S minus S,- where8,- represents the total desired distance of movement along the axisunder consideration.

For the case of a relatively long move as represented in FIG. 4, theoperation of the control system may be represented by curve 50. Thecurve 50 includes an acceleration portion 51 where speed isprogressively increasing, a rapid traverse portion 52 where speed isrelatively constant and a deceleration portion 53 where speed isdecreased to zero. Where a tachometer provides an output of voltage as afunction of speed, this output voltage is measured to provide theordinate in the graphical representation of FIG. 4. From FIG. 4, it willbe observed that the load moves a distance 8, as it accelerates fromrest to the rapid traverse speed. Similarly, the load moves a distance SD as it decelerates from the rapid traverse speed essentially to therest condition. The distance the load travels at the rapid traversespeed is represented by the symbol S in FIG. 4, and the total distancetravelled is represented by S The voltage from the tachometer while theload is travelling at the rapid traverse speed is indicated by thesymbol V, in FIG. 4.

The other case of interest is that where the distance to be travelled Sis sufficiently short so that the load does not attain the rapidtraverse speed. This is represented in FIG. 5 by the curve 55 includingan acceleration portion 56 and deceleration portion 57. Where the lessthan the deceleration distance 8,, of FIG. 4. Thus the computer mustdetermine a distance 8,,- which will be equal to S in the case of amovement where rapid traverse speed is attained as in FIG. 4, and whichwill be equal to S, in the event that rapid traverse speed is notattained, for example as represented in FIG. 5.

In a preferred embodiment in accordance with the present invention, thecontrol system is itself operable to determine its own operatingcharacteristics from which the value 8,, or S, can be computed withreference to each input command to be executed by the control system.

For the purpose of enabling the control system to determine thenecessary parameters, certain components are included in the system asindicated in FIGS. 1 and 2. Simply by way of example selector switchcontacts 60a, 60b (FIG. 1) and 60c (FIG. 2) are shown which are closedmanually or under computer control when the control system parametersare to be observed. Re-

ferring to FIG. 1, status flag flip-flops 61 and 62 are provided forcoupling to the outputs respectively of pulse amplifiers I1 and 12.Thus, status flag 6] will be set by each count pulse produced by apositive increment of movement of the load, and status flag 62 will beset in response to each count pulse representing a negative incrementofmovement of the load. NOR

gates 63 and 64 are shown coupled to respective outputs of theflip-flops 61 and 62 so as to supply an interrupt signalat output line65 or 66 for signalling the computer that one of the flip-flops is inthe set condition. The computer, then successively tests selectorcomponents such as 71 and 72 to determine the cause of the interruptsignal. For example if flag component 61 is in set condition, NAND gate73 will be enabled, and a "SKIP" signal will be transmitted fromselector l7l to output line 74 leadingto the computer. Similarly, ifflag component 62 is in set condition, NAND gate 75 is enabled so thatthe signal from selector component 72 will be transmitted as a SKIP"signal at output line 76. When the computer has determined the cause ofthe interrupt condition, the computer actuates the corresponding clearselector component 78 or 79 so as to reset or clearthe clag componentwhich was in the set condition.

This logical structure of FIG. 1 enables the computer to observe thesuccessive count pulses and to determine the polarity of such pulsesduring its testing of the control system to determine its operatingcharacteristics.

FIG. 2 illustrates circuit components which enable thetiming of certaintest operations on the control system. These components may include, forexample, an eight kilohertz oscillator component 81, and a clock statusflag flip-flop 82. So long as switch contact 600 is closed flip-flop 82willbe set at intervals for 125 microseconds, causing an interruptsignal to be supplied to the computer via line 84 from NOR component 85.With the status flag component 82 in set condition, NAND gate 87 isenabled so as to transmit a SKIP" signal to output line 88 when thecomputer activates the associated test selector component 89. When thecomputer detennines that the clock status flag component 82 is the causeof the interruption, the computer will then activate the associatedclear selector component 90 so as to clear the clock status flagcomponent 82. Thus the circuit of FIG. 2 enables the computer to observeand count a series of clock pulses to provide a time base to itsobservation of the operating characteristics of the control system.

Having outlined the general characteristics of a preferred embodiment ofthe present invention, the background considerations, details ofpractical mechanization, and operation of the system will now bediscussed.

DISCUSSION OF THE ILLUSTRATED CONTROL SYSTEM The following criteria wereadopted in order to generate the desired control technique: l thecontrol system should be general in nature so that it could apply to anymachine tool, (2) the control system should have the ability to adapt toa change of characteristics, and (3) it should be capable of toleratingunlimited controllable overshoot in positioning to a given coordinate.Two primary problems which had to be solved in implementing the newconcepts were: I) how to determine the proper point to begin thedeceleration, and

(2) what procedure should be followed if the desired is to use on-offdeceleration control by means of a small I general purpose digitalcomputer, such as described in the copending applications. The benefitsrealized being that: (I) a digital computer determines the decelerationpoint, not an arbitrary factory adjustment, (2) the computer may be usedto close the control loop, thus saving hardware cost, and (3) numericalprogramming effort can be significantly reduced by using the computer asa combination calculator and tape preparation facility The digitalcomputer, through the use of previously stored program, can detenninethe proper deceleration point by experimentally interrogating themachine tool and measuring the acceleration distance (8,) anddeceleration distance (S These experimentally derived values would thenbe available either for use by the computer or by external hardware toposition the machine tool. The advantage of using a computer toaccomplish this task is that it can be repeated either periodically orat any time at the discretion of the operator, should machine toolcharacteristics change because of equipment replacement of load change,or should be control system be applied to other unrelated machine tools.

These are two possible conditions to be considered in trying todetermine the deceleration boundary:

Digital peeition position feedback is available in the a form ofdiscrete pulses from a Trump Ross rotary trans- I ducers connected tothe carriage leadscrew. The transducers provide two amplified squarewave pulse trains, each being 50 counts per revolution shifted ninetydegrees'out of phase. The direction of travel and linear count pulsesmust be obtained by properly decoding move and the distance required tostop using maximum a deceleration is fairly constant deviations beingnonlin- .earities in the machine tool. Therefore. for the case where thedesired move (S is t (S il-S the computermerely beginsthe move and waitsuntil the reg lmaining distance is less than or equal to S then at-thisM f point the machine tool'is commanded to stop, using maximumdeceleration. I l Case2, S L S +S (see FIG. ).,Thesecond case ina I]volves a'condition where the desired move (8,) read p frornpunched tapeisfless than the sum of the accelerate ying anddecelerating distances.in this case the deceleration point is dependentf'on the size of theproposed move. Actualgrphical recordings, typified by FIGS. 6 and "I,show the machine'tool's output response in relaion to condition of Case2. Because of the dynamics of he sym r acceleration and the decelerationcurves 92 and '93., FIG. 6 and 94m 95, FIG. 7, may

10 FIG. 1 illustrates two control lines 28 and 29 which I theinformation presented by the transducers. Decoding Network are used tosignal the control system as to the direction and amount of movement inpositioning toa given -coordinate. The direction of travel is determinedby the ordered sequence in which the pulses from the transducer areobserved. A device which will operate as a pulse decoder approximatelyis designated as type R601 and ,is manufactured by the Ditigal EquipmentCorporation. in order to operate, a ground levelmust precede a pulsechange to ground by 400 nanoseconds;

this'provid'es an idealdecoding network when connected, as shown in thefourth figure of the pending applications. Positive pulses appear at theoutput of one.

beapproxi'rnated byparabolas which are substantially linear near theprincipal axis. Because of this observal tion an approximation was madewhichgreatlysimplifled the'calculation of the deceleration point forvariou sizemoves. Theapproxirnation assumes the slope of theacceleration and deceleration curves near the prin- 1 cipal-axis to belinearfBased on this 'asumption, the followingresult can derived forthe: deceleration dis- I where K, and K, are'the slope l a n the timerequired for the load to accelerateto rapid traceleration' slopeK, islarger thanlg becasue-of the presenceof output dampingin'the presentcontrol sys- R60l amplifier (11, FIG. 1), while negative pulses appearat the output of the other R601 amplifier (12, FIG. I). Since everyleading or trailing edge of the transducer output generates a uniquepulse, 200 pulses are generated per revolution of the leadscrew,producing on pulse for every one thousandth of an inch of linear travel.Digital Computer A general purpose PDP8/S digital computer, alsomanufactured by the Digital Equipment Corporation, is specified to beused in the control loop, to 1) sample the actual system in ordertodetermine the decelera tion, and (2) to actually provide appropriatesignals to control point to point positioning. Digital to AnalogConverter a The purpose of the digital to analog converter(3l,

7 FIG. 3) is to accept discrete digital signals from the verse speed,and rgisfthe required for deceleration essentiallyto a rest condition{tom such speed. The detern, andthis tends toi'niprove over-alliresponseby perining fasterdeceleration when compared to Systems .jwith nooutputdam i g Y "The preferred control system has "the' advantage ofmajor components, namely (1) digital transducers, (2) a decoderand pulsegenerating network."(3) edigital computer. (4) digital to analogconverters, (5 ),a servo fiamplifier, and (6) a-DC drive motor. a a (Thespecific components employed in the system are described as follows(with reference numerals in parenthesis referring to thepresc-ntdrawings where app p iate) Digital Transducers being used notonly to determine acceleration; and a a celeration characteristics butalsoto position the machine tool. Thepositioningloop is comprisedof sixcomputer (e.g. counter 30, and logic 38, FIG. 3), and

provide an appropriate analog voltage to be used as an I input by theservo amplifier (25, FIG. 3). Thespecified component for this operationis an A601 digital to anament Corporation. Servo Amplifier The-componentspecified (25, P16. 3) is manufactured by Hughes lndustral Controls andis the same type as that used in Hughes numerical controls. It is lSOwhich saturates at an output voltage of volts. The amplifier receivesinput signals from the digital to analog converter, also manufactured bythe Digital Equipment Corporation.

The component specified (25, FIG. 3) is manufacQ tured by hughesIndustrial Controls and isthesame type as that used in Hughes numericalcontrols. it is a shunt wound motorcan be used. The motor is made forlog converter. also manufactured by the Digital'Equiphalf wave SCRamplifier having a gain of approximately of providhalf wave operationand requires 75 volts for the armatur'e, 50 volts for the field and runsat a speed of I725 R PM at these stated conditions.

FIG. l showsa portion of the hardware necessaryto interfacea machinetoolfto aPDP8/S digitalcomputer.

needs adigital clock 81, FIG. 2) with a frequency of approximately 8kilohertz.

both for the purpose of determining machinejt'ool char-t.

acteristics and to assistin closing the control loop. Transducerpulsesfare shaped and reduced to standard "jgxlogic levelsthroughthe useof twow50l Schmitt trigflgers whose'outputs are used by R60l pulsedecoders.

f-T he -R601 pulseamplifiers (II andl2) controltwosta- (from'conductor'l t or I76), andt'he next sequential *programinstruction will beskipped. e e

* no.3 illustrates the method the computer uses to provide inputs to theservo amplifier 25 in order to pcsition the machine tool. The gain ofthe servo amplifier wareQand-if the device beingltested caused aninter-f I rupt. a signalwill be present on the computerskip bus At thestart of atest calculation. the computer initializes all the internalcounters. turns on the interrupt sys- I item, closes switches 60a. 60band 60c, and applies a voltalge to the servo amplifier 25 sufficient todrive the motor at full speed; The computer then waits for a clock orcountpulse program interrupt. Upon receiving interrupts.clock pulsesoccurring between count pulses 1 are stored in computer memory locations(C) and CH) where a comparison is made to determine if any twocountpulse intervals occur within one clock pulse of each other. If so. themachine tool is assumed to be traversing at constant maximum traversespeed. At this point counter B in thecomputer memory will contain thenumber of clockpulses, and counter S (acceleration distance will containthe number of count pulses is adjusted so that a display of one count intheerror digital tofanalog'cjonverttar 31 which causes a minimum tem isrunning under a rapid traverse conditiomthe register produces a DCvoltage at the output of the a f movement tomake a correction. Thus.when the sys- I servo amplifier 25 receives a command input only from.

' Digital Equipment CorporationWOSO orWldrivers (23 or 24). Whenthetdeceleration point(S#$ r-S has been reachedan d therapid traverse inputhas been removed.th'e system is'decelerated-rapid.y. Final positioningis underthe control of the error count supplied to the digital to analogconverterlil. I a

Q Maintaining closed loop controlonce the rapid trawhen usingthefconverteris howto obtain linearity 1 verse input hasbeen removedinvolves the use of A601 1digital1'to analoggconverter stages(manufactured by Digital Equipment Corporation). A problem that arisesto achieve rapid traverse speed. and the machine tool g will make a moveof 5.000 inches before beginning deceleration. 4 r I f Duringdeceleration, the total numberof-clock pulses 'to stop is stored inrnemory location F. and counter 8 (deceleration distance) will containthe number of count pulses to complete deceleration. At this point thetest is completed and the machine, tool is assumed av.

rest if no count pulse occurs for approximately 2.5 'sec onds or20.000-clock pulses. e *1 It is a matter of routine to prepare acomputer program in accordance with FIG. 9 to carry out the test anddetermine the necessary information to use on-off deceleration control.

OPERATION OFTl-IE CONTROL SYSTEM'OF FIGS. 1 and 3 to ControlDeceleration The flowdiagram represented'in FIG. 10 shows how a systemaccording to FIG. 3 couldbe controlled using I the previously determinedinformatiom-The ,discisionwhen the count changes .from a plus onecount.(00 j .al) to aminus onecount (ll L l) and vice versa, re- Imemberingthat the computer. operates in 2's 'complement arithmetic. Thisis solved by proper application of the position count to the digitaltoanalog converter.

Thus thetmost significant stage 35 of the converter displaysthe=negation of the "sign bit, which normally isthe most significant bitofithe'error display register. It is this last connectionwhich allows 'abias voltage to be changewhen the errorregister changes polarity.

"Using thistechnique provides a linearmode of operavtion for smallerrors when used I; eration control concept.

a j OPERATION To DETERMINE MACHINE TOOL t Y CHARACTERISTICS FIG. 9 is aflow diagram used in the experimental determination of machine toolcharacteristics. The r scheme employs the useof an interruptsystem suchas that used by the PDPB/S digital computer. 'lnaddition with thenon-ofi' decel-.

to a machine tool and required interface. the computer process isextremely simple oncethe machine tool characteristics are known. Thecomputer merely reads a position coordinate from previously preparedpunched tape. and determines if the proposed move will cause thecarriage to attain a rapid traverse speed.

If so (see FIG. 4). the motor is driven at full speed until theremaining distanceto the objective is equal to 8,, (decelerationdistance), then the carriage isstopped as f I quickly as possible byremoving the rapid traverse input and allowing the converter 31 tocomplete positioning should a small overshoot or undershoot occur. Ifthe required command move'is less than the distance needed .to attainfull speed (see FIG. 5) the computer will compute the distance away fromthe command position where the input must be reduced to zero in order tominimize positioning time by solving the equation summed with theconverter output to produce a linear 5 a where K, and K, equal thecontents of B and F storage locations previously defined.

A reasonable and good approximately of the savings to be realized byusing the omoff deceleration control was obtained by recording thetachometer response with respect to time on a Brush recorder. FIG. 8shows an example of the typical results obtained. First. data wasobtained showing the acceleration and deceleration times for positioningto various size moves using conventional deceleration methods. Then,while the C machine tool was running at a rapid traverse speed, the Iservo command input was reduced to ground potential and the resultsrecorded. Using this simple procedure provides a rather good insightinto what can be expected when the on-off deceleration control method isfully implemented.

The results of this test showed that the on-off deceleration controlreduced the deceleration time by approximately 60 percent when comparedwith conventional methods. Reflected in the over-all time to positionand punch a hole. A Strippit Fabramatic 30/30 could punch 80 holes perminute on 1 inch centers, as opposed to 60 holes per minute whichpresently results from using conventional methods of controllingdeceleration.

It should also be remembered that since a digital computer is used inthe control loop. deceleration is not anarbitrary tuning procedure, butit is uniquely adapted to individual machine tools. always readilyavailable in the form of a computer program. Normal usage would includel initial installation, (2) periodic checking. Should machine toolcharacteristics change.

or (3) application of the control system to other machine tools.

ALTERNATIVE EMBODIMENTS As an alternative to the system heretoforedescribed. the computer could use its own core memory as a counter S tostore the distance remaining to the commanded end point i.e. (Sr-S). Thecomputer would then decrease the stored count by one each time a countpulse interrupt signal appeared at the count interrupt output line 65 or66, FIG. I. When the stored count reached S, the computer would load thecount S y into the stages of counter 30, which would then I22, FIG. 10a.and 123. FIG. 10b (found on sheet No.

5 of the drawings along with FIG. 10c), apply for the example where thecomputer core memory is used as a register 5 to store a count valueSr-S. When using the hardware shown in FIG. 3, these program steps areomitted and the decision steps of blocks 124, FIG. 10a and I25, FIG.10b. involve an interrogation of test selector 43e. FIG. 3.

The executive steps represented by block 130, FIG. 106 (found on sheetNo. 5 of the drawings). would include loading of 8,. (S or S into thebinary counter 30. FIG. 3. where the hardware of FIG. 3 is utilized tocount transducer pulses directly.

FIG. 11 shows an alternative to the operation indicated in FIG. 10c. andhas been specifically drawn to illustrate operation where the computeruses its core memory as a counter S to accomulate a count value equal tothe remaining displacement S S, of the axis I from its position at thebeginning ofa move. In this case the steps of blocks -123 of FIG. 10 beincluded:

For operation as represented in FIGS. Ila and 11b. switches 60a and 60b.FIG. 1, would be closed. and switch 60c. FIG. 2 would be open. Thecounter 30 would operate as a register. and switches (not shown) inlines 28 and 29, FIGS. 1 and 3, would be opened so that the counterwould not respond to transducer pulses directly. Flip-flop 47. FIG. 3would remain in the reset condition so that status flag flip-flop 43could not be actuated to set condition. In carrying out the function ofdecision block 124, FIG. 100. or 125, FIG. 10b. the computer wouldsimply compare the count stored in its register S with the value 8,, orS also stored in its core memory. When the count in the register S wasequal to the stored value S or 8,. the computer would begin executingthe steps represented in FIGS. lla and III). This is indicated by theuse of the circle with the character 28 therein at the output flow lines141 and I42 of decision blocks 124 and 125, FIGS. 10a and 10b. and atthe input flow line 143 to function block 144, FIG. Ila.

The step of block 144, FIG. 11a. would be executed by the computer byactuating the clear selector 27,

FIG. 3. Block 145, FIG. Ila. would be executed by transferring thecontents of register S to the various stagcs of'counter 30. FIG. 3. Asrepresented by components 146 and 147 in FIG. lla. an interrupt wouldoccur only with the setting of status flag flip-flop 61 or 62, FIG. 1.

The function of block 148, FIG. lla. may be carried out by having thecomputer determine if the count in register S has previously passedthrough zero. (See blocks 151. I60 and 161 whose mechanization will bedescribed hereinafter) In block 149, the computer would respond to anovershoot pulse by adding an absolute value of one to a register 08 inthe computer core memory. In carrying out block 150, the computer wouldsubstract a count from the register S More particularly component I50serves toadd each count pulse to register S in accordance with itspolarity so that the register maintains an algebraic count at all timesin accordance with the displacement of the load from the commanded endpoint. even when the load has overshot the commanded end point. (Thiscan be done since the computer can determine whether status flip-flop 61or 62. FIG. I. has been actuated to represent the count pulse.)

Having reference to block 151. FIG. Ila. it will be noted that theprocedural steps of FIG. Ila are repeated as indicated by flow line 152until the count registered by the computer in register S is zero. atwhich time control moves to the sequence of FIG. llb.

Referring to block 160, FIG. llb. it will be noted that in the event ofa further count pulse. control is transferred to the block 161 todetermine if the count pulse following the condition Sr-O has thepolarity of the command being executed. If the polarity reflectsmovement in the commanded direction. the pulse would constitute anovershoot pulse. For the particular logic illustrated. it may be assumedthat once an overshoot has occurred. the computer will store this factand answer the interrogation at block 161 and a block 148 in theaffirmative throughout the remainder of the positioning cycle. Also theobservation of an overshoot condition by the computer will causeovershoot pulse to be registered as negative counts (i.e. as counts ofopposite polarity) in register S For example if the register S initiallyis counting down from a given positive 13 displacement value overshootpulses will be registered as negative values in two's complementnotation. Any count pulses occurring after the overshootwill be registerin the OS register of the computer core memory regardless of whether thecount pulse results from movement in the overshoot direction or in thereturn direction. Thus. the actual value of the overshoot will be equalto one-half the final value registered in the location OS of thecomputer memory. Thecounter 30 will be controlled during an overshoot soas to register successive counters representing the overshoot just asthough it were responding directly to transducer pulses.

From block 162, FIG. lib. control passes to block 150 whereby thefurther count is algebraically applied to the previous count ofthe'register S Thus after a first overshoot pulse the count in registerS will be a value applied to this register. Since S is equal to one,control now passes via flow line 152, FIG. Ila, back to block 145, withfurther count pulses being applied as absolute values to the OS counteras indicated by block 149, and being applied algebraically to theregister S as indicated by block 50. t

The illustrateed logic assumes that there will not be an oscillationabout the end point value once an overshoot has occurred. Of course.oscillation after an overshoot could be taken into account byalgebraically applying counts to the OS register as well as to the Sregister.

Once the load returns to the commanded end point andS is again equal tozero, it may be assumed that the logic will follow the path 160,165-469. The operation of block 165 may be performed by means ofcomponents such as illustrated in the eighteenth Figure of ser. No.744,372.

With the system of FIG. ii, the computer corrects the value of S aftereach move so as to correct it for many changes in the operatingcharacteristics of the particular machine tool with which the computeris associated. Where the initial command has been less than the sum S-i-S the blocks 168 and 169 may represent the correction of futurevalues of S, so as to tend to eliminate overshoot for example by anappropriate modification of the constant K, stored by the computer.Anydesired formula may be used for computing adjusted values of S1 and Sto insure that a stable optimum adjustment will be maintained for agiven machine tool.

' With respect to each of the embodiments, it will be understood thatthe maximum output from the digital to analog converter 31 is far lessthan the output from driver 23 and 24. Further, a speed responsivetachometer is connectedto line 180, FIG. 3, and this tachometer willsupply a feedback voltlage when the rapid traverse movement of the loadis interrupted which feedbackvoltage will be sufficient in many cases tosaturate the amplifier 25 will a reverse polarity current so as toprovide very rapid braking action or plugging on the drive motor.Normally, the accuracy of the system is such that the digital to analogconverter 31 need comprise only a relatively few stages, so that thelinear range of the converter will correspond to error counts in thevicinity of zero. For example. the linear range of the converter wouldcorrespond to error counts of less than plus or minus l6.

I claim as my invention:

. l. The method of operating a computerized numerical control systemwherein a machine tool control includes an external hardware counter forreceiving pulses representing successive increments of movement of aload. and a minicomputer is connected on line with said machine toolcontrol, which method comprises operating said minicomputer to respondto a displacement command specifying movement to a commanded end pointto generate a deceleration distance signal representing a decelerationdistance at which the load is to be decelerated in order to bepositioned at the commanded end point. operating said minicomputer toactuate said machine tool control for producing movement toward saidcommanded end point,

monitoring said external hardware counter to determine when saidhardware counter has received a total number of pulses corresponding tomovement to a point location a distance equal to said decelerationdistance in advance of said commanded end point, and

operating said minicomputer in response to reaching said point toactuate said machine tool control to progressively reduce the velocityof movement so as to stop said load at the commanded end point.

2. The method of operating a computerized numerical control systemwherein a machine tool control includes an external hardware counter forreceiving pulses representing increments of movements of a load. and aminicomputer is connected on line with said machine tool control, whichmethod comprises operating said minicomputer to respond to adisplacement command representing a distance of movement less than thatin which the load is to achieve maximum speed and to generate anacceleration distance and a deceleration distance to be traversed inresponse to respective acceleeration and deceleration commands suppliedby the minicomputer to the machine tool control such that the total ofthe acceleration distance and the decelera tion distance will equalthedistance represented by said displacement command. operating saidminicomputer to supply to said machine tool control said accelerationcommand to accelerate the load, monitoring said external hardwarecounter to determine when the acceleration distance has been traversedby the load, and operating the minicomputer thereafter to apply saiddeceleration command to said machine tool control for decelerating saidload as it traverses said deceleration distance. v

3. The method of determining characteristics of a control system whichcomprises 1 driving the system at a predetermined speed and de velopingmotion pulses in response to successive increments of movement thereof,

shifting the system to a deceleration mode and generating clock pulsesduring deceleration of the system, and

counting such motion pulses and such clock pulses during deceleration ofthe system to detennine the time and distance required to bring thesystem substantially to a stop so as to obtain parameters for use indetermining an optimum deceleration point for the control system.

4. The method of claim 3 further comprising storing the parameters soobtained and automatically applying the stored parameters to determinethe deceleration point in subsequent moves executed by the controlsystem.

5. The method of operating a control system which comprises 1 ing theresponse of the system to a subsequent move,

and adjusting the stored characteristics in accordance with suchobservations so as to take account of subse quent changes in theoperating characteristics of the individual control system.

7. A machine tool control system comprising a machine tool controlincluding an external hardware counter (30, HO. 3) for receiving pulsesrepresenting successive increments of movement of a load duringexecution of a given displacement command,

a minicomputer (200, FIG. 12) connected on line with said hardwarecounter (30) and operable to receive said displacement command and tocompute a deceleration point in advance of the end point to which theload is to be moved in executing the displacement command,

an electric drive circuit (25) responsive to a maximum input signal toaccelerate the load toward a rapid traverse operating speed,

bistable drive control circuitry (21-24, FIG. 3) connected with saidelectric drive circuit (25) for selectively supplying said maximum inputsignal to said electric drive circuit (25), and shiftable between afirstbistable condition where said maximum input signal is applied to saidelectric drive circuit (25) and a second bistable condition where saidmaximum input signal is removed,

drive control selector circuitry (20, 27, FIG. 3) connected with saidminicomputer (200) and with said bistable drive control circuitry(21-24), andoperable in response to a first signal from saidminicomputer to place said bistable drive control circuitry (21-24) insaid first bistable condition to cause the acceleration of the load tothe rapid traverse operating speed, and operable in response to a secondsignal from said minicomputer (200) to shift said bistable drive controlcircuit (21-24) to the second bistable condition,

a bistable counter condition circuit (38, 43, 45, 46, FIG, 3) connectedwith said counter (30) and shiftable between first and second bistableconditions, and responsive to a predetermined count condition of saidcounter (30)to shift from the first bistable condition to said secondbistable condition. and

counter condition sensing circuitry (43b, 43e) connected with saidminicomputer (200) and with said bistable counter condition circuit (38,43, 45, 46) and responsive to a predetermined selection signal from theminicomputer (200) to transmit a counter condition signal to theminicomputer (200) in accordance with the bistable condition of saidbistable counter condition circuit (38, 43, 4, 46),

the minicomputer being in control of rapid traverse movement of the loadby means of said counter condition circuit (38, 43, 45, 46) and saiddrive control selection circuitry (20, 27) and being operable by meansof said drive control selector circuitry (20, 27) to intervene duringexecution of the displacement command to initate deceleration of theload for stopping thereof at the commanded end point, whereby thedeceleration point may be changed in accordance with changes in theoperating characteristics of the system during its useful life.

8. A machine tool control system in accordance with claim 7 with saiddrive circuit (25) comprising a servo amplifier whose output directcurrent signal controls the speed of operation of the load.

9. A machine tool control system in accordance with claim 8 withtachometer means responsive to the spced of movement of the load andsupplying a feedback voltage to said servo amplifier and operable forproducing a braking action when rapid traverse movement is interrupted.

10. A machine'tool control system in accordance with claim 7 with adigital to analog converter (31, P10. 3) connected with said counter(30) and having its output connected with said electric drive circuit(25) for controlling positioning of the load when the bistable drivecontrol circuitry (21-24) has been shifted to said second bistablecondition.

11. A machine tool control system in accordance with claim 8 with adigital to analog converter (31) connected with said counter for controlthereby and having its output connected with said servo amplifier (25)in parallel with said bistable drive control circuitry (21-24) forcontrolling the speed of operation of the load when said bistable drivecontrol circuitry (21-24) is in said second bistable condition.

12. Amachine tool control system comprising a machine tool controlincluding a minicomputer (200, P10. 12) having storage means (61, 62,FIG. 1) for receiving pulses representing successive increments ofmovement of a load,

an electric drive circuit including a servo amplifier (25, FIG. 3)responsive to a maximum input signal to accelerate the load toward arapid traverse operating speed and responsive to progressively reducedinput signal levels to correspondingly reduce the speed of movement ofthe load,

bistable drive control circuitry (21-24, FIG. 3) connected with saidservo amplifier (25) for selectively supplying said maximum input signalthereto, and shiftable between a first bistable condition where saidmaximum input signal is applied and a second bistable condition wheresaid maximum input signal is removed,

drive control selector circuitry (20, 27, FIG. 3) connected with saidminicomputer (200) and with said bistable drive control circuitry(21-24), and operable in response to a first signal from saidminicomputer (200) to place said bistable drive control circuitry(21-24) in said first bistable condition to cause the acceleration ofthe load to rapid traverse operating speed, and operable in response toa second signal from said minicomputer (200) to shift said bistabledrive control circuit (21-24) to the second bistable condition, and adigital to analog converter circuit (30, 31, FIG. 3) connected with saidminicomputer (200) and with said servo amplifier (2S) and operable tosupply progressively reduced input signal levels to the servo amplifier(25) once the bistable drive control circuitry (21-24) has been shiftedto said second 17 bistable condition to progressively decelerate saidoad,

the minicomputer (200) being in control of the duration of the rapidtraverse movement by virtue of its connection with said drive controlselector circuitry (20, 27), and being in control of the deceleration ofthe load by means of its connection with saiddigital to analog convertercircuit (30, 31), whereby the deceleration point may be changed by theminicomputer (200) in accordance with changes in the operatingcharacteristics of the system during its useful life.

13. A machine tool control system in accordance with claim 12withtachometer means (180, FIG. 3) responsive tothe speed of movement ofthe load and supplying a feedback voltage to said servo amplifier (25)and opeable for producing a braking action when rapid traverse movementsis interrupted.

14. A machine tool control system in accordance with claim 12 with saiddigital to analog converter (30, 31) having a generally linear range ofoutput for a range of input count values of less than plus or minussixteen.

15. A machine tool control system in accordance with claim 12 with anoscillator (81, FIG. 2) connected with said minicomputer (200) forsupplying timing pulses to the minicomputer (200) and thereby enablingthe minicomputer (200) to determine when the spacing between pulsesrepresenting successive increments of movement of the load correspond tothe rapid traverse operating speed.

16. A machine tool control system in accordance with claim 12 with saidmachine tool control including a transducer direction and rate sensingcircuit (10, FIG. 1) connected with saidstorage means (61, 60, 62) forsupplying said pulses representing successive increments of movement ofthe load thereto, and a feedback condition sensing circuit (71, 73, 72,75, FIG. 1) connected with said bistable pulse receiving circuit (61,62) and with said minicomputer (200) and incluging a feedback conditionselector circuit (71, 72, FIG. l) rcsponsive to a selection signal fromsaid minicomputer (200) to transmit a feedback condition signal to theminicomputer (200) in accordance with the condition of said storagemeans (61, 62).

1. The method of operating a computerized numerical control systemwherein a machine tool control includes an external hardware counter forreceiving pulses representing successive increments of movement of aload, and a minicomputer is connected on line with said machine toolcontrol, which method comprises operating said minicomputer to respondto a displacement command specifying movement to a commanded end pointto generate a deceleration distance signal representing a decelerationdistance at which the load is to be decelerated in order to bepositioned at the commanded end point, operating said minicomputer toactuate said machine tool control for producing movement toward saidcommanded end point, monitoring said external hardware counter todetermine when said hardware counter has received a total number ofpulses corresponding to movement to a point location a distance equal tosaid deceleration distance in advance of said commanded end point, andoperating said minicomputer in response to reaching said point toactuate said machine tool control to progressively reduce the velocityof movement so as to stop said load at the commanded end point.
 2. Themethod of operating a computerized numerical control system wherein amachine tool control includes an external hardware counter for receivingpulses representing increments of movements of a load, and aminicomputer is connected on line with said machine tool control, whichmethod comprises operating said minicomputer to respond to adisplacement command representing a distance of movement less than thatin which the load is to achieve maximum speed and to generate anacceleration distance and a deceleration distance to be traversed inresponse to respective acceleeration and deceleration commands suppliedby the minicomputer to the machine tool control such that the total ofthe acceleration distance and the deceleration distance will equal thedistance represented by said displacement command, operating saidminicomputer to supply to said machine tool control said accelerationcommand to accelerate the load, monitoring said external hardwarecounter to determine when the acceleration distance has been traversedby the load, and operating the minicomputer thereafter to apply saiddeceleration command to said machine tool control for decelerating saidload as it traverses said deceleration distance.
 3. The method ofdetermining characteristics of a control system which comprises drivingthe system at a predetermined speed and developing motion pulses inresponse to successive increments of movement thereof, shifting thesystem to a deceleration mode and generating clock pulses duringdeceleration of the system, and counting such motion pulses and suchclock pulses during deceleration of the system to determine the time anddistance required to bring the system substantially to a stop so as toobtain parameters for use in determining an optimum deceleration pointfor the control system.
 4. The method of claim 3 further comprisingstoring the parameters so obtained and automatically applying the storedparameters to determine the deceleration point in subsequent movesexecuted by the control system.
 5. The method of operating a controlsystem which comprises operating the control system to determinepredetermine characteristics thereof, and storing such characteristics,and responding to subsequent commands taking into account the storedcharacteristics with respect to the given individual control system. 6.The method of claim 5 further comprising observing the response of thesystem to a subsequent move, and adjusting the stored characteristics inaccordance with such observations so as to take account of subsequentchanges in the operating characteristics of the individual controlsystem.
 7. A machine tool control system comprising a machine toolcontrol including an external hardware counter (30, FIG. 3) forreceiving pulses representing successive increments of movement of aload during execution of a given displacement command, a minicomputer(200, FIG. 12) connected on line with said hardware counter (30) andoperable to receive said displacement command and to compute adeceleration point in advance of the end point to which the load is tobe moved in executing the displacement command, an electric drivecircuit (25) responsive to a maximum input signal to accelerate the loadtoward a rapid traverse operating speed, bistable drive controlcircuitry (21-24, FIG. 3) connected with said electric drive circuit(25) for selectively supplying said maximum input signal to saidelectric drive circuit (25), and shiftable between a first bistablecondition where said maximum input signal is applied to said electricdrive circuit (25) and a second bistable condition where said maximuminput signal is removed, drive control selector circuitry (20, 27, FIG.3) connected with said minicomputer (200) and with said bistable drivecontrol circuitry (21-24), and operable in response to a first signalfrom said minicomputer to place said bistable drive control circuitry(21-24) in said first bistable condition to cause the acceleration ofthe load to the rapid traverse operating speed, and operable in responseto a second signal from said minicomputer (200) to shift said bistabledrive control circuit (21-24) to the second bistable condition, abistable counter condition circuit (38, 43, 45, 46, FIG. 3) connectedwith said counter (30) and shiftable between first and second bistableconditions, and responsive to a predetermined count condition of saidcounter (30) to shift from the first bistable condition to said secondbistable condition, and counter condition sensing circuitry (43b, 43e)connected with said minicomputer (200) and with said bistable countercondition circuit (38, 43, 45, 46) and responsive to a predeterminedselection signal from the minicomputer (200) to transmit a countercondition signal to the minicomputer (200) in accordance with thebistable condition of said bistable counter condition circuit (38, 43,4, 46), the minicomputer being in control of rapid traverse movement ofthe load by means of said counter condition circuit (38, 43, 45, 46) andsaid drive control selection circuitry (20, 27) and being operable bymeans of said drive control selector circuitry (20, 27) to interveneduring execution of the displacement command to initate deceleration ofthe load for stopping thereof at the commanded end point, whereby thedeceleration point may be changed in accordance with changes in theoperating characteristics of the system during its useful life.
 8. Amachine tool control system in accordance with claim 7 with said drivecircuit (25) comprising a servo amplifier whose output direct currentsignal controls the speed of operation of the load.
 9. A machine toolcontrol system in accordance with claim 8 with tachometer means (180)responsive to the speed of movement of the load and supplying a feedbackvoltage to said servo amplifier and operable for producing a brakingaction when rapid traverse movement is interrupted.
 10. A machine toolcontrol system in accordance with claim 7 with a digital to analogconverter (31, FIG. 3) connected with said counter (30) and having itsoutput connected with said electric drive circuit (25) for controllingpositioning of the load when the bistable drive control circuitry(21-24) has been shifted to said second bistable condition.
 11. Amachine tool control system in accordance with claim 8 with a digital toanalog converter (31) connected with said counter for control therebyand having its output connected with said servo amplifier (25) inparallel with said bistable drive control circuitry (21-24) forcontrolling the speed of operation of the load when said bistable drivecontrol circuitry (21-24) is in said second bistable condition.
 12. Amachine tool control system comprising a machine tool control includinga minicomputer (200, FIG. 12) having storage means (61, 62, FIG. 1) forreceiving pulses representing successive increments of movement of aload, an electric drive circuit including a servo amplifier (25, FIG. 3)responsive to a maximum input signal to accelerate the load toward arapid traverse operating speed and responsive to progressively reducedinput signal levels to correspondingly reduce the speed of movement ofthe load, bistable drive control circuitry (21-24, FIG. 3) connectedwith said servo amplifier (25) for selectively supplying said maximuminput signal thereto, and shiftable between a first bistable conditionwhere said maximum input signal is applied and a second bistablecondition where said maximum input signal is removed, drive controlselector circuitry (20, 27, FIG. 3) connected with said minicomputer(200) and with said bistable drive control circuitry (21-24), andoperable in response to a first signal from said minicomputer (200) toplace said bistable drive control circuitry (21-24) in said firstbistable condition to cause the acceleration of the load to rapidtraverse operating speed, and operable in response to a second signalfrom said minicomputer (200) to shift said bistable drive controlcircuit (21-24) to the second bistable condition, and a digital toanalog converter circuit (30, 31, FIG. 3) connected with saidminicomputer (200) and with said servo amplifier (25) and operable tosupply progressively reduced input signal levels to the servo amplifier(25) once the bistable drive control circuitry (21-24) has been shiftedto said second bistable condition to progressively decelerate said load,the minicomputer (200) being in control of the duration of the rapidtraverse movement by virtue of its connection with said drive controlselector circuitry (20, 27), and being in control of the deceleration ofthe load by means of its connection with said digital to analogconverter circuit (30, 31), whereby the deceleration point may bechanged by the minicomputer (200) in accordance with changes in theoperating characteristics of the system during its useful life.
 13. Amachine tool control system in accordance with claim 12 with tachometermeans (180, FIG. 3) responsive to the speed of movement of the load andsupplying a feedback voltage to said servo amplifier (25) and opeablefor producing a braking action when rapid traverse movements isinterrupted.
 14. A machine tool control system in accordance with claim12 with said digital to analog converter (30, 31) having a generallylinear range of output for a range of input count values of less thanplus or minus sixteen.
 15. A machine tool control system in accordancewith claim 12 with an oscillator (81, FIG. 2) connected with saidminicomputer (200) for supplying timing pulses to the minicomputer (200)and thereby enabling the minicomputer (200) to determine when thespacing between pulses representing successive increments of movement ofthe load correspond to the rapid traverse operating speed.
 16. A machinetool control system in accordance with claim 12 with said machine toolcontrol including a transducer direction and rate sensing circuit (10,FIG. 1) connected with said storage means (61, 60, 62) for supplyingsaid pulses representing successive increments of movement of the loadthereto, and a feedback condition sensing circuit (71, 73, 72, 75,FIG. 1) connected with said bistable pulse receiving circuit (61, 62)and with said minicomputer (200) and incluging a feedback conditionselector circuit (71, 72, FIG. 1) responsive to a selection signal fromsaid minicomputer (200) to transmit a feedback condition signal to theminicomputer (200) in accordance with the condition of said storagemeans (61, 62).